Friday, February 15, 2013

How Stressed is Your Goldfish?

How
Stressed is Your Goldfish? Taking a Closer Look at the Ornamental Aquarium Trade

By: Morgan Ivens-Duran

A
couple of weeks ago, my research lab came into possession of a beautiful blue
beta fish that was left over from an experiment in an undergraduate Animal
Behavior class. I was thrilled. My desk is positioned next to a previously
empty fish tank that had been left behind by a previous generation of graduate
students, and for months I had gazed upon this desolate, barren 25 cubic liter
environment. That afternoon, I went to a local aquarium shop to pick out some
companions for our new lab mascot.

Years
ago in my high school Honors Biology class, I had been given the responsibility
of maintaining a fish tank and frequently visited a local aquarium shop to
replace those that had fallen ill to some sort of disease or parasite. At the
time, I hadn’t stopped to think much about where these small creatures had come
from. Now, after years of educating myself about conservation issues and
reading scientific literature about various anthropogenic impacts on the marine
environments, as I looked around the small, brightly lit shop with tanks
containing multitudes of brightly colored fishes, I stopped to think about what
these fish might have gone through during their journey from their native reefs
to the present moment.

Approximately
2,000 species and millions of individual organisms are sold each year in the
ornamental fish trade, whose value is estimated at around $900 million US
dollars. Sixty percent of these ornamental fish are destined for US aquarium
owners, and while many individuals are now obtained from commercial production
facilities, a significant portion is still sourced from the wild. The aquarium
trade is comprised of roughly equal proportions of fresh and saltwater fish,
the latter of which are primarily collected from coral reefs in tropical
Southeast Asian countries such as Thailand, Indonesia, and Singapore. In recent
years, there has been a shift from aquaria containing only ornamental fish to the
creation of miniature reef ecosystems, which has dramatically increased the
diversity of species and magnitude of the ornamental aquarium trade as
aquarists now purchase live coral and invertebrates in addition to showy,
ornamental fish. This dependence on coral reef ecosystems, which are already subject
to a variety of other anthropogenic impacts, is both a blessing and a curse.
While continued exploitation depletes local populations and harvesting practices
are often destructive, these habitats represent a tangible economic resource
that could spur conservation measures in ways that more abstract ecosystem
services might not.

While
as a marine ecologist I find all of this fascinating, this blog is about
organismal physiology, not marine conservation issues. So, having set the stage,
lets get into some of the details of how the aquarium trade affects the
organisms that pass through it every day. In particular, I want to discuss the
physiological reasons underlying the high rates of mortality seen in the aquarium
industry.

In
the 1950’s, up to 50% of the fish collected would die during collection, and on
average an additional 30% would die at each step along the chain of custody. While
mortality rates are no longer quite that high, a significant number of organisms
still die along their journey from their native waters to your local pet store.

Diagram showing the typical chain of custody for fish in the aquarium trade, both wild-collected and farmed. From Livengood and Chapman (2008).

Because
of the immense scale of the aquarium trade and the difficulty of replicating
travel conditions in a laboratory setting, pinning down the exact causes of
this widespread mortality has been difficult. However, within the last decade
or so findings from a variety of studies have begun to illuminate the complex
combinations of stressors that result in the death of so many ornamental fish
and associated creatures.

Handling
stress, poor water quality during shipment, and periodic severe stressors have
all been shown to increase mortality of ornamental fish. Although the use of
toxic chemicals such as cyanide in reef fish collection is declining, it has
not yet disappeared. Exposure to cyanide for as little as 2 minutes has been
shown to cause damage on a cellular level and impair physiological function due
to extensive damage to tissues in the liver, kidney, spleen, and brain. The
physical act of handling fish during collection can also increase stress. Reef
fish often secrete a thin layer of mucus that provides an important buffer
against osmotic stress. Even mild abrasions can disrupt that protective shield,
increasing the sensitivity of the fish to the fluctuating water conditions that
often follow. During transport, the water can oscillate between extremes of
temperature, light exposure, and pH. Crowding not only limits mobility, but
also causes both a rapid buildup of toxic nitrogenous wastes produced by the
teeming masses of fish and decreases in the levels of dissolved oxygen. Unfortunately,
well-intentioned attempts by fishers to change the aqueous environment of these
fish can have deleterious consequences. Tlustly et al. (2005) followed a supply
route of cardinal tetras (Paracherodon
axelrodi) from the Rio Negro in Brazil to their final destination, the New
England Aquarium in Boston, MA. They found that when the piabeiros added new water to the 10-liter casapas used to transport the tetras, the pressure of that fresh
water hitting the fish was enough to stun or even kill them.

Since
most fish in the aquarium trade suffer from poor water quality in addition to
the occasional shock of the containing crate falling over or being dropped, is
it any wonder that individuals from many species don’t survive the multi-day journey?

Given
the picture I’ve just painted above, it may seem that the odds are
overwhelmingly against any given fish in the aquarium trade surviving the
topsy-turvy voyage that is the global aquarium trade. However, some species
seem to be more resistant to these types of stressors. One notable example is
the pot-bellied seahorse (Hippocampus abdominalis).

In mammals,
stressful situations induce the release of corticosteroids. In invertebrates,
the stress response involves the release of adrenaline from chromaffin cells in
the kidney, which causes the breakdown of glycogen into glucose (a form of chemical
energy) as well as an increase in heart rate, respiration rate, and the
oxygen-carrying capacity of the blood. Collectively, these types of responses
are known as the sympathetic nervous system, or in more colloquial terms, “the flight
or fight response.” Wright et al. (2007) set out to see if this classic stress
response was evident in the pot-bellied seahorse when exposed to common
stressors in the aquarium trade such as handling and confinement. Surprisingly,
it seems that the sedentary nature of this animal prevents the stress response
seen in so many other ornamental aquarium species.

However,
this singular example does little to counteract the overwhelming magnitude of
species that are ill-suited for inclusion the aquarium trade, at least in its
current state of regulation. Although there are a variety of ongoing efforts by
both organizations within and external to the aquarium industry pushing for stronger
regulations, ultimately it is up to us as consumers to create the economic
incentive for companies to combat the rampant mortality rates currently
plaguing the industry.

That
afternoon, as I stood in that small shop, I am sorry to admit that I noticed
the large tank of live coral, representing decades if not hundreds of years of
growth in a far away tropical sea. I noticed the various wild-collected
tropical fishes and prawns and anemones. But rather than voice my concerns, I
picked out three brightly colored guppies and a few aquatic plants and went
about my business. If there was a silver lining, it is that my experience that
afternoon prompted me to research this topic in far more detail than I ever had
before, and to write this blog post in the hopes that the next time we visit a
shop to purchase a new addition for our tank, we will do so with our eyes pried
open a little wider.